Budget cuts being debated in Congress could prompt DOE to revise its goals, he said. Depending on how much money lawmakers devote to Yucca, the schedule could be pushed back months or longer.

Until the budget is resolved, Sproat said, "I will not be able to answer the question with certainty whether I will be able to get a license application in by June 30, or whether I will be able to get a licensing application in by 2008."

Other timelines for the program, which envisions burying 77,000 tons of high-level nuclear waste 100 miles northwest of Las Vegas, also are being reconsidered, he said. Though DOE has said its best-case scenario has a repository open by 2017, many experts think a more realistic date could be 2025 or later.

DOE officials long have tied the fate of the planned Nevada repository to their ability to score money from Congress to build a $57 billion dollar complex. But Thursday marked the first time a DOE official publicly raised the idea of backing away from the one date the department had advertised with confidence.

The comments suggest that project opponent Sen. Harry Reid, D-Nev., is causing pain by wielding a budget sword to attack the project.

Reid, the Senate majority leader, reportedly is seeking to cut the Yucca budget to below $400 million, much less than the $494.5 million that President Bush requested at the start of the year to keep it on schedule.

Talks continued Thursday on a massive year-end spending bill that would contain funding for the energy project and thousands of others throughout the government.

One Yucca Mountain critic said he did not believe Sproat.

Bob Loux, director of the Nevada Agency for Nuclear Projects, said the DOE official was delivering a Chicken Little-style distress call as a move to marshal allies in Congress.

"I don't buy it," Loux said. "I think that is a lot of hype. He is trying to drive a lot of guys on Capitol Hill to make sure his cuts are not that deep."

Loux said he thought the agency would be able to meet the June deadline "even if their budget was $250 million."

The Energy Department announced its new schedule in July 2006. Explaining it to a House committee that month, Sproat said the licensing date was a near-certainty. He said June 30, 2008, falls on a Monday, "and I do not plan on working that weekend."

The message of certainty was designed to comfort lawmakers and nuclear industry executives who had grown tired of the agency missing deadlines. A government repository was supposed to have opened a decade ago, and subsequent goals have been shelved because of legal, technical and management problems.

In January, DOE official Christopher Kouts hinted at an industry conference that the latest repository effort could be the last if the department failed to meet its application deadline.

"We need to deliver by 2008, or else there will be a substantial restructuring of the program and perhaps a new direction. My sense is that we will deliver," said Kouts, who since has become the No. 2 manager for Yucca Mountain, behind Sproat.

"I just think that everybody knows we need to deliver this time, and that is what we are driving very hard to do," Kouts told reporters after his speech.

Charles Pray, an nuclear adviser to the governor of Maine, said the Energy Department might be able to shift funding from other projects or find other ways internally to boost the Yucca repository if Congress cuts the budget.

Pray said that officials from states that want nuclear waste removed from reactor sites and relocated to Nevada would tend to blame members of Congress if the Energy Department misses deadlines because of budget cuts.

"It has to rest with them if the department has said this is what we need to meet the deadlines and Congress cuts them by 25-30 percent, and they can't meet those deadlines," Pray said.

Contact Washington Bureau Chief Steve Tetreault at stetreault@stephensmedia.com or (202) 783-1760.